Method of increasing enzyme stability and activity for pulp and paper production

Abstract

Wood pulp is treated with an esterase formulation in combination with a metal ion or cationic polymer to increase the stability or activity or both of esterase enzymes at high temperature, or at extreme pH ranges of acidic and alkaline conditions. The treatment by esterase together with metals ion or cationic polymer can be used to treat pitch containing pulp at high temperatures prior to, during or after refining of wood chip / pulp, in order to enhance the reduction of pitch problems and facilitate in the manufacture of paper.

Description

FIELD OF THE INVENTION[0001]The present invention is generally in the field of managing wood pitch using enzyme treatment of wood pulp.BACKGROUND OF THE INVENTION[0002]Wood resin is composed of fatty acids and resin acids, triglycerides, steryl esters, and sterols. Wood resins, as well as other extractives such as lignins, pectins, and phenols, are the major components of pitch deposits. During mechanical pulping, the encapsulated resin is liberated from ray parenchyma cells and resin canals. Some of the dispersed resin droplets precipitate onto fiber surfaces, impairing fiber to fiber bonding and thereby negatively affecting the physical properties of the pulp. Dispersed resin which precipitates later in the pulping and papermaking processes can affect paper machine runnability and reduce paper quality, resulting in increased manufacturing costs.[0003]Traditionally, pitch deposits in pulping and paper manufacturing processes have been reduced by seasoning wood logs and chips, and b...

AI Technical Summary

Benefits of technology

[0015]A method of treating pitch containing pulp at a higher temperature range than what the esterases allow at normal application temperature or pH has been developed. In one embodiment pitch containing pulp is treated with an effective amount of metal ions selected from the group consisting of aluminum, calcium, magnesium, iron, copper, zinc, titanium and zirconium prior to treatment with a lipolytic enzyme formulation. In another embodiment pitch containing pulp is treated with an effective amount of a cationic polymer. In a more preferred embodiment the pulp is treated with an effective amount of alum. The pulp is treated with an effective amount of a metal ion or cationic polymer effective to increases stability of the enzyme at high temperature and at broad pH ranges of 3-11.

[0018]The wood pulp can be treated for a period of time from about 0.1 to 36 hours, more preferably from about 1.0 to about 12 hours. The addition of metal ions or cationic polymers to the pulp prior to enzyme treatment stabilizes the enzyme formulation and speeds up the enzymatic reactions at high temperature and broader pH range. This enhances the effectiveness of the enzyme formulation in removing extractives such as long chain triglycerides whose conversion is favored thermodynamically at high temperatures. Additionally, the ability of the enzyme formulation to be active at high temperatures decreases the need for adding cooling water prior to enzyme treatment, thus reducing the fresh water use and costs associated with waste waster treatment. Furthermore, the ability of the enzyme formulation to be active at lower pH (as low as 3.0) and higher pH (as high as 10.5) reduces the need for acid or base usage for pH adjustment of pulp stocks prior to enzyme treatment. It makes it possible for enzyme to be added to the locations where the conditions can be too harsh for normal lipolytic enzymes with the use of method described herein. In addition, the chemical costs can be reduced.

Problems solved by technology

Some of the dispersed resin droplets precipitate onto fiber surfaces, impairing fiber to fiber bonding and thereby negatively affecting the physical properties of the pulp.

Dispersed resin which precipitates later in the pulping and papermaking processes can affect paper machine runnability and reduce paper quality, resulting in increased manufacturing costs.

However, those traditional methods have their limitations due to the complexities of pulping and paper making process, particularly when used with recycled paper.

Such treatments, however, can result in increased concentrations of certain pitch components and by-products, such as fatty acids, which would affect machine runnability and product quality.

In fact, one of the major challenges in modern mills with closed-cycle water systems is the removal of lipophilic wood extractives that tend to accumulate in pulping and papermaking systems or circuits because they can no longer be sufficiently purged from the system via the water.

The increasing degree of water closure in mills is leading to an increase in pitch concentrations, which increases the chances of pitch deposition and the discharge of more heavily concentrated pitch-laden waste water.

This makes it more difficult for pulp and papermaking mills to meet state and federal requirements for reducing effluents to meet minimum effluent discharge levels.

However, many mechanical pulping mills are operated at physical and chemical conditions where current commercially available, “normal” enzymes will be deactivated and lose their functions or activities.

Thus the application of normal lipolytic enzymes disclosed in the prior art is limited or even impossible at such high temperatures.

The additional cooling creates many problems, for example, temperature shock to the system, increased fresh water usage, and increased demand of a mill's wastewater treatment capacity.

The addition of cooling water can cause energy loss in a mill.

If the stock consistency is lowered, the mill won't have enough storage space to store pulp stocks.

Therefore, in many mills, lowering the TMP operating temperature to male the enzyme work is simply not viable.

Lipolytic enzymes, being mostly surface-active enzymes, won't work effectively since the TGs and pitch remain solid under temperature ranges where the normal enzymes are active.

Additionally, solubility and miscibility of fatty acids and their corresponding salts increase with temperature.

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